A. Field of the Invention
This invention relates in general to components of an automatic temperature control system for automobiles.
B. Description of the Prior Art
Automatic temperature control systems were first introduced in about 1964 in the United States and are now available on most large size cars. In the systems heretofore, the components of the system have been scattered throughout the car, being interconnected by vacuum and wiring harnesses. One of these systems, for instance, has a main component grouping on the power servo, with other hardware located on the dash control, in ducts, on the air conditioning case, and in the engine compartment. Another has many components grouped on the heater-air conditioning case, with other components on the dash control, under the dash and in the engine compartment. These systems are generally complicated, difficult to install and maintain, expensive to produce and inaccurate.
The components of such systems and their function is as set forth below:
1. Sensors--to sample in-car and ambient temperature;
2. Transducers--to convert the sensors' output to a control signal;
3. A power servo--to convert the control signal to a stroke, thereby driving program switches and a temperature door. Bimetal sensors have been used to sense temperature changes and provide a signal responsive thereto for many years. However, the signal from such a sensor is very small and is rarely able to provide the necessary force to activate a mechanical or electrical system of which the sensor is a part;
4. Program switches--to control system functions such as air discharge location, blower speed, recirculation, water valve, on-off function, etc.;
5. A temperature blend door--to modulate the air discharge temperature from the heater-air conditioning system;
6. Dash controls--contains levers used by the driver of a car to adjust and set the system to the desired mode and condition of operation;
7. Selector switches--operated by the dash controls;
8. Cold engine lockout (CELO) valve--to delay the system operation in its heater mode until the heater core is warm;
9. Compressor ambient switch--to control the compressor operation as a function of the ambient temperature;
10. A water valve--controlled by a program switch to turn water off to the heater core under maximum cooling conditions; and
11. A resistor block--contains a dropping resistor for fan speed control. This works in conjunction with the program switches.
There are many problems associated with these systems.
In operation, these systems generally have two sensors which individually sense the ambient and in-car temperature and convert these readings to either electronic or mechanical signals. The ambient signal is used to bias the in-car signal and the single output is used to control the operation of the system. The appropriate temperature is generally supplied by the operation of a temperature door whose opening and closing regulates the heat and air conditioning supplied from the heater and air conditioner.
Since the sensors are often mounted at the end of long tubes supplying the in-car and ambient air, error in the sensing apparatus is often introduced by the air passing through long super-heated stretches which bias the temperature of the incoming air. For instance, the in-car air is often sampled by letting air enter a tube which is underneath the dash. By the time the air reaches its sensor near the fire wall, the temperature of the air in the tube has often reached an elevated temperature to that of the original air by reason of bias occurring when the air passed through heated areas under the dash. This problem has sometimes been corrected by placing both sensors at the spot where sampling air was taken in, but this requires long electrical leads and electrical conversion signals for changing the temperature of the air sensed to an appropriate electrical value.
In these systems, the output stroke of the power servo is proportional to the vacuum level therein which in turn is proportional to the sensor signals from the two sampling devices. This is called a "proportional vacuum" system. A proportional vacuum system is subject to stroke hysteresis, i.e., there may be two different output strokes at the same vacuum level. As the transducer signal does not have a feedback loop, the sensors and transducers combination does not know where the servo motor stroke is at any given time, which causes drift, cycling and over-shoot.
Hysteresis is caused by the frictional forces required to drive the program swithches, to open the temperature doors, by the override springs, and by various pin hole tolerances. Further, hysteresis is not constant from one system to another and will deteriorate with time.
In these prior art systems, as the vacuum level increases, the servo motor strokes towards maximum air conditioning mode operation while with decreasing vacuum the servo motor drives towards maximum heater condition. The friction in the system, however, causes the stroke to reach different positions for the same temperature, depending on whether the vacuum is increasing or decreasing. Current systems take two steps to alleviate these conditions and effect acceptable control. One is to provide high vacuum levels so that the slope of the control curve increases. This serves to decrease the differences in stroke for the same temperature. The second means used is to provide low friction program switches. These two means do serve to reduce hysteresis, but they present problems themselves in that the use of high vacuum level is hard to attain on the present-day automobiles with their numerous pollution control devices, especially on long hill climbs and the use of low friction switches is expensive.
There are two types of vacuum motors, or power servos, currently used to supply output to a shaft from a supply of vacuum. These are often used to operate car doors, as well as to drive switches in an automatic temperature control system. Generally, these motors consist of two case halves (the cylinder) which entrap a diaphragm upon which is mounted a rigid piston with an output shaft. One case half has a port connected to a source of vacuum and the other half is open. As vacuum is varied through the port, the motor strokes towards and away from the case half containing the port.
One type of such motor is called a rolling diaphragm motor and the other is the flip-flop diaphragm motor.
Vacuum switches or valves are used in automotive applications in an on-off mode to apply vacuum to various places within the system to open and shut air supply doors, etc. In the automatic temperature control system of the present invention, vacuum switches are used for such things as determining the air discharge location, blower speed, recirculation operation mode, water valve operation, etc. Several types of such switches are presently on the market, all of which have certain disadvantages.
One type is generally made of two die case pieces which are lapped smooth. Ports are provided in one half while the other has channels so that when the second half is rotated it either provides a channel from one port to the other so that vacuum can be switched from one port to another, or its closes the ports. These switches have generally required a fairly high force to overcome friction and cross-venting of the ports has resulted in serious vacuum leakage and loss of vacuum, especially on long hill climbs. This loss of vacuum causes a loss of control in all of the vacuum systems.
Another such switch has the movable portion made of rubber, which is molded to a metal plate. Here the switch has very small ports, on the order of 0.020 inches, with relatively large rubber sealing contact areas. The small size of the ports often allows blockage due to frost or accumulation of dirt.
In my copending U.S. Pat. Nos. 4,063,682; 4,206,645; 4,269,351; 4,291,717 and 4,426,913; apparatus is shown for an improved automatic temperature control system for automobiles whereby the operator may set a desired in-car temperature and the control system will operate the heater and air conditioning systems to keep the in-car temperature at the selected mark.
Such apparatus provides an accurate means of maintaining the selected temperature by eliminating frictional losses and providing for low hysteresis, in reducing the amount of vacuum required from the engine, and by negating the inaccuracies of return springs. It eliminates certain electrical relays and override springs, thereby cutting complexity and cost. It groups the components in a single module at the fire wall so that under-dash congestion is reduced and a compact, easily producible, relatively inexpensive, module type system is attained. The module concept allows system calibration at the factory and easier servicing once the car is in use since all important elements are under the hood in one place. Further, this system allows low vacuum operating levels and option possibilities such as variable blower speed; high blower coming on when engine is started under hot soak start-up conditions; diagnostic functions for vacuum, electrical and automatic operations; and low blower come-on under cold soak start-up condition.
The ambient and in-car air is fed through a delivery tube wherein the in-car air is biased by the ambient air so that only a single temperature sensor is required. The sensor directly drives a vacuum-vent valve mounted on the output member of a vacuum-assist motor, thereby monitoring the relative position of the sensor and the vacuum assist output and physically moving with the stroke of the motor to form a feedback loop. This valve applies vacuum or vent to the assist motor to drive the stroke to its proper position and thereby maintain the desired temperature in the car. The stroke of the vacuum-assist motor operates various switches causing the operation of the system components, such as the temperature blend door, the CELO valve, the water valve, etc. Thus this is a proportional stroke system, as opposed to the prior art proportional vacuum systems.
The sensor is attached to the long end of an input link which is normally in a horizontal position. When the sensor moves because of a change in in-car or ambient temperature, the vacuum-vent valve is activated by reason of the mechanical advantage in the linkage. This activation causes the valve to change the vacuum level in the vacuum-assist motor, causing it to stroke to such a position, against spring force, that the linkage is again brought to its horizontal rest position, whereupon the system again comes to rest.
The entire system comprises only three cables, twelve electrical contacts, ten vacuum connections (serving eight functions) a cold engine lockout switch, the double walled tube, and the control module. Using this module system where all the components are grouped in one place greatly increases the reliability of the total system, e.g., less parts are required, the hysteresis losses are minimized, there are fewer external electrical and vacuum connections, etc.
Also shown and described in the referenced patents are improved components of the system. One vacuum-vent valve used to control the vacuum-assist motor in the feedback loop is of a novel "H" valve type wherein twin diaphragms are provided in the valve to negate the effect of a single diaphragm on the valve's operation. A balance chamber is provided so that both diaphragms see the same vacuum level.
Another vacuum vent valve shown and described is of a flapper valve type. Here too the input link is directly connected to the bimetal sensor, which causes the valve to vary the vacuum input to the vacuum-assist motor and thus vary the output stroke of this motor.
A new vacuum-assist motor, generally of the rolling diaphragm type, is shown wherein the cylinder wall is sloped to increase the stroke, with the same case depth, and allow for a shallower overall motor to be used.
Reference may be had to the patents mentioned above for a further detailed description of the temperature control system and components thereof.
According to the present invention, a new rotary vacuum valve or switch is described wherein twin contact lines on the movable part of the valve eliminates cross venting from port to port and wherein the wiper blades can take more out-of-flatness without leaking.